One Rep Max Calculator
Estimate your one-rep max (1RM) from any set you’ve done, and see a full percentage breakdown for programming your training.
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These are estimates, not guarantees. Actual 1RM depends on technique, fatigue, and lift experience — use the percentage table as a training guide, not an exact prediction.
How 1RM Is Estimated
Lifting to true failure for a single rep is risky and hard to test often, so these formulas estimate your 1RM from a lighter set of multiple reps. They tend to be most accurate in the 1–10 rep range.
No single formula is perfect for everyone — some run slightly high, others slightly low, depending on the lift and your rep range. Averaging all three, as this calculator does by default, tends to smooth out individual formula bias.
Frequently Asked Questions
How accurate is an estimated 1RM?
It’s usually within a few percent of your true 1RM when the set is done with good form and taken close to failure, especially for sets of 10 reps or fewer. Accuracy drops the higher the rep count goes.
Why does the estimate change depending on the formula?
Each formula was developed from different research data sets and lifts, so they weight reps slightly differently. The differences are usually small at lower rep counts and grow larger as reps increase.
How do I use the percentage table for training?
Strength programs are often written as a percentage of your 1RM — for example, “work up to 3 sets of 5 at 80%.” Once you know your estimated 1RM, you can find the matching weight for any prescribed percentage directly in the table.
Is it safe to actually test my true 1RM?
Testing a true 1RM carries more injury risk than submaximal sets, especially without a spotter or coach. Most lifters only need to test it occasionally with proper warm-up and supervision — estimating from a lighter set is safer for regular use.